Generally, a resin composition employed for a large injection molded article radiating lots of heat such as a computer housing or other office devices necessarily maintains flame retardancy and heat resistance and high mechanical strength. In order to provide the resin composition with flame retardancy, conventionally, a halogen-based flame retardant and an antimony compound have been used. However, since combustion gases generated by using the halogen-based flame retardant are hazardous for a human body, there is a need for a resin composition including halogen-free flame retardant.
The commonly-used method for providing flame retardancy without using the halogen-based retardant is to employ a phosphate ester-based flame retardant. U.S. Pat. No. 4,692,488 discloses a halogen-free phosphorus-based compound, and U.S. Pat. No. 5,061,745 discloses a monomer-type phosphate ester. A resin composition, however, can exhibit a “juicing” phenomenon wherein a flame retardant of a monomer-type phosphate ester compound is transported onto a surface of the article and precipitated during the molding process.
An oligomer-type phosphate ester compound is also known to be used as a flame retardant, and a method of preparing the compound is disclosed in Japanese Patent Laid-Open Publication No. 59-202,240. In addition, the compound may be used as the flame retardant of a polyamide or polycarbonate resin. U.S. Pat. No. 5,204,394 discloses a flame retardant resin composition including an aromatic polycarbonate resin, a styrene-containing copolymer or a graft copolymer, and a phosphate ester oligomer.
Using an oligomer-type phosphate ester flame retardant with a thermoplastic resin can reduce the juicing phenomenon and relatively improve heat resistance compared to a monomer-type phosphate ester. An oligomer-type phosphate ester flame retardant, however, can have reduced flame retardancy as compared to a monomer-type phosphate ester-based flame retardant having the same weight. Thus higher amounts of the oligomer-type phosphate ester flame retardant may be required to ensure comparable flame retardancy. This, however, can significantly deteriorate mechanical strength of the resin composition.
European Patent No. 640,655 discloses a PC/ABS resin composition including a mixture of an aromatic polycarbonate resin, a vinyl-based copolymer, a graft copolymer, a monomer-type phosphate ester, an oligomer-type phosphate ester and a fluorinated polyolefin. The composition, however, can exhibit the juicing phenomenon of transporting a monomer-type phosphate ester onto a surface of an article during the molding process, the heat resistance can be deteriorated, and the flame retardancy can be deteriorated when using an excessive amount of the oligomer-type phosphate ester.
Thus, the present inventors have developed a flame retardant thermoplastic resin composition that can have excellent flame retardancy, heat resistance and mechanical strength and also can have excellent property balance of impact resistance, thermal stability, workability, and appearance characteristics, and the like, in order to solve the problems.